The present invention relates to a bin for composting vegetable matter such as lawn and garden waste and to the method of its use. More specifically, the bin is of a type that can be readily assembled from modular parts and equally readily disassembled to permit quick and ready access to the contained composting material.
Composting lawn and garden waste serves a dual purpose for the home resident. It provides a way to dispose of bulky waste such as lawn clippings, hedge trimmings, vegetable-type kitchen scraps, etc. Further, the resulting compost is a valuable soil amendment. It adds organic matter to the soil without imposing significant nitrogen or other nutrient demand. This is particularly important in sandy or clayey soils. The addition of compost improves tilth in heavy clay soils and water holding capacity in sandy soils. The organic portion of the soil also plays a critical function in ion exchange between mineral nutrients in the soil and plant root structures.
Compost formation is caused by bacterial and fungal action, especially on the cellulosic and other carbohydrate portions of the plant residues. It can proceed under either moist aerobic or anaerobic conditions, although the former is much to be preferred. Thermophilic and other aerobes are particularly efficient at reducing plant wastes to a rich humus. Aerobic decomposition generally proceeds much faster and is essentially without odor. Depending on a number of factors, plant wastes can be composted under highly aerobic conditions in periods ranging from a few weeks to several months. This same process with similar vegetal matter can take years under anaerobic conditions. Aerobic composting results in emission of water and carbon dioxide with considerable heat being produced. Temperatures in actively composting plant wastes can rise to levels in the neighborhood of 65.degree. C. (150.degree. F.) or even higher. Some of the composting microflora are adapted to thrive and multiply under these elevated temperatures. The higher temperatures are very desirable because the composting action is greatly accelerated and weed seeds and plant and soil pathogens are killed.
Since compaction occurs as a compost pile builds up and as material decomposes, aeration tends to become poorer, especially in the interior portions. In these compacted volumes the action of the obligate aerobes causing the composting slows significantly. Ultimately the aerobic microflora would be replaced by anaerobic microflora. These not only act slowly but give off methane and obnoxious gases containing reduced sulfur compounds. Serious home gardeners usually ensure good aeration by periodically turning over the composting material to restore a loose and permeable structure. This might be done several times during the composting period on a given pile of plant wastes. It is a general rule that, within reason, the more times an active compost pile is turned over the faster the process will proceed and product uniformity will be better. The serious gardener will manage the bed and determine turnover times by measurement of the internal temperature profile over time, according to known procedures. Unfortunately, for the average gardener turning over a compost pile involves relatively heavy work and considerable lifting. Normal bins are usually a rectangular wooden structure that may or may not have one open or partially open side. As the composting material is shoveled or forked out, access to the material in the bottom becomes difficult. Some existing bins are made with hinged sides so that the bin can be completely stripped from the pile to enable easier turnover. These tend to be heavy and awkward and have not found general acceptance. Other strippable bins are made of wire screening, such as poultry wire. This is prone to deformation during use and kinking upon removal. These screen bins do permit better aeration than closed-sided bins but suffer from accelerated moisture loss which slows composting.
Commercial composting operations have long been in operation to produce growing medium for crops such as mushrooms. These formerly used large quantities of animal manures. More recently they have used other agricultural wastes such as corn cobs and stalks, surplus or spoiled hay and similar plant materials, as well as sludge from bioponds. These materials are usually piled in long windows on the ground and frequently turned with large machines to ensure good aeration. A machine of this type is shown in U.S. Pat. No. 3,856,276.
Many types of home composting bins have been proposed and some are sold commercially. U.S. Pat. No. 3,654,903 describes equipment for growing earthworms and simultaneously producing a compost leachate, commonly called "compost tea". This system would seem to be poorly adapted for the gardener growing anything more extensive than house plants.
U.S. Pat. No. 3,951,294 describes a compost bin composed of interlocking modular units that slide together vertically. The sidewalls may be perforated or may be constructed from screens held in marginally located frames. These frames interlock side-to-side by sliding together vertically. They can also be built up in a one-above-the-other fashion using a pin and socket locking arrangement. A related divisional patent, U.S. Pat. No. 4,125,394, shows one version that apparently has a snap-on lid.
U.S. Pat. No. 4,105,412 describes a composter which again is primarily adapted for making a compost tea or "sap". The composting plant material is held within a perforated corrugated structure which is surrounded by an imperforate shell similar to a bottomless garbage can. A tight lid covers the device. Water is periodically poured through the composting plant waste and the "sap" is collected in a pail underlying the upper portion of the structure. While the preferred embodiment would be essentially anaerobic, one version shows a structure of simple spaced apart horizontal wood slats resting on the bottom pail. One of the bottom slats may be omitted to permit "mining" the compost after it is formed.
U.S. Pat. No. 4,184,602 shows a modular multipanel system useful for storage of grain or other materials and also useful for composting bins. Two identical panels are hinged along their edges. The panels have regularly spaced notches along their upper and lower transverse edges. These notches serve to accommodate clips that can combine the panel modules into various configurations.
A simple enclosure of wire screen panels is shown in U.S. Pat. No. 4,211,033. The panels are relatively rigid and self supporting and can be formed into enclosures of various shapes and sizes.
U.S. Pat. No. 4,352,888 describes another modular composting bin made of molded plastic panels. These are joined end-to-end by vertically sliding together a molded rod and hook arrangement. Slots are provided in the sidewalls to provide limited aeration. Telescoping flanges on the top and bottom of the panels provide a snap together arrangement for increasing the height of the bin. There is no ready provision for removing compost except from the top.
U.S. Pat. No. 4,683,674 shows a composting bin of modular molded plastic units similar in many ways to the one just described. Provision is made here for doors on the sides of the panels. These ostensibly permit removal of compost from any level although, depending on the size of the bin, this would be difficult using any tool larger than a garden trowel. The doors seem better adapted for use of the bin as a vertical planter. One figure shows an entire lower panel absent for compost removal from the bottom. How this panel would be removed, in view of the interlocking construction, is not described.
A simple wood frame supported screen wire enclosure that can be readily opened to give access to the composting material is described in a Pierce County (Washington) Master Gardeners Bulletin. In principle this is similar to the enclosure of U.S. Pat. No. 4,211,033. While simple wire containers of this type can ultimately produce compost, the exterior portion of the pile is exposed to ambient air and wind which results in rapid heat and moisture loss from the surface. This can be sufficient to slow or almost stop aerobic composting action. On the other hand, bins made of wood, plastic, or metal frequently inhibit access by fresh air to much of the surface of the composting mass. This can result in an anaerobic environment within the stack of material.
A number of commercially available or home made composters use a tumbling or rotary action to speed the composting process. Several of these are compared with stationary composters in an article by Charles Nardozzi, National Gardening, Sep./Oct. 1991, pp 38,39, and 65. Most of these are small and of very limited capacity.
While all of these prior known composting bins would have greater or lesser usefulness, none of them fully address the problem of simplifying the turnover of substantial amounts of the contained composting plant material to achieve rapid aerobic composting. The present invention is particularly well adapted for dealing with the problem of compost turnover and for making compost very rapidly and efficiently with considerably reduced manual effort.